I used to own an '87 Accord. I installed a wood floor in the trunk. The box was then secured to the wood floor with metal brackets, so I could remove it without too much trouble, but it didn't slide around when installed.
In the wood floor I had a door that allowed access to the spare. I use the same type of hinge used on pianos for the lid that covers the keys.
It was a pretty sweet setup. I had 3 amps mounted to the back of the sub enclosure, and a carpeted panel with cutouts for the heatsinks that attached to the back of the enclosure. The wiring was all hidden under the carpeted panel that extended from the floor of the trunk to the rear deck, and from side to side. Half of my trunk was useable, the other half devoted to stereo.
Only once did I have to use the door to get to the spare, but I was sure glad I went to the trouble of installing it and keeping the spare.